diff --git a/.changeset/wise-projects-update.md b/.changeset/wise-projects-update.md
new file mode 100644
index 0000000..164d3d4
--- /dev/null
+++ b/.changeset/wise-projects-update.md
@@ -0,0 +1,5 @@
+---
+"t3code-cli": minor
+---
+
+Add `project update` for editing project metadata.
diff --git a/README.md b/README.md
index d96dfca..ee2a430 100644
--- a/README.md
+++ b/README.md
@@ -154,6 +154,7 @@ pnpm sync-upstream --target stable
 ```sh
 t3cli project list                        # List known projects
 t3cli project add [--path <path>] [--title <title>]
+t3cli project update [--project <ref>] [--title <title>] [--workspace-root <path>] [--provider <id>] [--model <slug>] [--option <key=value>] [--reasoning-effort <value>] [--effort <value>] [--fast-mode | --no-fast-mode] [--thinking | --no-thinking] [--clear-default-model] [--thread-env local|worktree | --clear-thread-env] [--favicon <path> | --clear-favicon] [--format auto|human|json]
 t3cli project delete [--project <ref>] [--force] [--yes]
 ```
 
diff --git a/src/application/project-commands.ts b/src/application/project-commands.ts
index 7069590..12dfe06 100644
--- a/src/application/project-commands.ts
+++ b/src/application/project-commands.ts
@@ -45,19 +45,19 @@ export const makeProjectDeleteCommand = Effect.fn("makeProjectDeleteCommand")(fu
 export const makeProjectMetaUpdateCommand = Effect.fn("makeProjectMetaUpdateCommand")(
   function* (input: {
     readonly projectId: string;
-    readonly scripts: Extract<
-      ClientOrchestrationCommand,
-      { readonly type: "project.meta.update" }
-    >["scripts"];
-  }) {
+  } & Omit<
+    Extract<ClientOrchestrationCommand, { readonly type: "project.meta.update" }>,
+    "type" | "commandId" | "projectId"
+  >) {
     const crypto = yield* Crypto.Crypto;
+    const { projectId, ...patch } = input;
     return {
       type: "project.meta.update",
       commandId: CommandId.make(
         `t3cli:project-meta-update:${yield* crypto.randomUUIDv4.pipe(Effect.orDie)}`,
       ),
-      projectId: ProjectId.make(input.projectId),
-      scripts: input.scripts,
+      projectId: ProjectId.make(projectId),
+      ...patch,
     } satisfies Extract<ClientOrchestrationCommand, { readonly type: "project.meta.update" }>;
   },
 );
diff --git a/src/application/projects.ts b/src/application/projects.ts
index caf5f9b..a3f02b3 100644
--- a/src/application/projects.ts
+++ b/src/application/projects.ts
@@ -4,9 +4,18 @@ import * as Path from "effect/Path";
 
 import { CliRuntime } from "../cli/runtime/service.ts";
 import { T3Orchestration } from "../orchestration/service.ts";
-import { ProjectCreateVisibilityError, ProjectLookupError } from "../domain/error.ts";
+import {
+  ProjectCreateVisibilityError,
+  ProjectLookupError,
+  ProjectUpdateValidationError,
+} from "../domain/error.ts";
 import { findProjectById, resolveProjectScope } from "../domain/helpers.ts";
-import { makeProjectCreateCommand, makeProjectDeleteCommand } from "./project-commands.ts";
+import {
+  makeProjectCreateCommand,
+  makeProjectDeleteCommand,
+  makeProjectMetaUpdateCommand,
+} from "./project-commands.ts";
+import { resolveModelSelection } from "./model-selection.ts";
 import { waitForShellSequence } from "./shell-sequence.ts";
 import type { T3ProjectApplicationService } from "./service.ts";
 
@@ -69,11 +78,83 @@ export const makeProjectApplication = Effect.fn("makeProjectApplication")(functi
     const dispatch = yield* orchestration.dispatch(command);
     return { projectId: input.projectId, dispatch };
   });
+  const updateProject: T3ProjectApplicationService["updateProject"] = Effect.fn(
+    "T3ApplicationLive.updateProject",
+  )(function* (input) {
+    const project = yield* resolveProject(input.projectRef);
+    let workspaceRoot = input.workspaceRoot;
+    if (workspaceRoot !== undefined) {
+      if (!input.local && !path.isAbsolute(workspaceRoot)) {
+        return yield* Effect.fail(
+          new ProjectUpdateValidationError({
+            message: "--workspace-root must be absolute for a remote environment",
+            projectId: project.id,
+          }),
+        );
+      }
+      workspaceRoot = input.local
+        ? path.resolve(cliRuntime.cwd, workspaceRoot)
+        : path.normalize(workspaceRoot);
+    }
+    if (input.favicon !== undefined && input.favicon !== null) {
+      const supported = /\.(?:avif|gif|jpe?g|png|svg|webp)$/i.test(input.favicon);
+      if (
+        path.isAbsolute(input.favicon) ||
+        input.favicon.split(/[\\/]/).includes("..") ||
+        !supported
+      ) {
+        return yield* Effect.fail(
+          new ProjectUpdateValidationError({
+            message: "--favicon must be a workspace-relative supported image path",
+            projectId: project.id,
+          }),
+        );
+      }
+    }
+    let defaultModelSelection = input.defaultModelSelection;
+    if (input.provider !== undefined || input.model !== undefined || input.options !== undefined) {
+      defaultModelSelection = yield* resolveModelSelection({
+        start: {
+          message: "",
+          ...(input.provider !== undefined ? { provider: input.provider } : {}),
+          ...(input.model !== undefined ? { model: input.model } : {}),
+          ...(input.options !== undefined ? { options: input.options } : {}),
+        },
+        project,
+        serverConfig: yield* orchestration.getServerConfig(),
+      });
+    }
+    const command = yield* makeProjectMetaUpdateCommand({
+      projectId: project.id,
+      ...(input.title !== undefined ? { title: input.title } : {}),
+      ...(workspaceRoot !== undefined ? { workspaceRoot } : {}),
+      ...(defaultModelSelection !== undefined ? { defaultModelSelection } : {}),
+      ...(input.defaultThreadEnvironment !== undefined
+        ? { defaultThreadEnvironment: input.defaultThreadEnvironment }
+        : {}),
+      ...(input.favicon !== undefined ? { favicon: input.favicon } : {}),
+    }).pipe(Effect.provideService(Crypto.Crypto, crypto));
+    const dispatch = yield* orchestration.dispatch(command);
+    const snapshot = yield* waitForShellSequence({ sequence: dispatch.sequence }).pipe(
+      Effect.provideService(T3Orchestration, orchestration),
+    );
+    const updated = findProjectById(snapshot, project.id);
+    if (updated === null) {
+      return yield* Effect.fail(
+        new ProjectLookupError({
+          message: `project not found after update: ${project.id}`,
+          ref: project.id,
+        }),
+      );
+    }
+    return { dispatch, project: updated };
+  });
 
   return {
     loadShell,
     addProject,
     resolveProject,
+    updateProject,
     deleteProject,
   } satisfies T3ProjectApplicationService;
 });
diff --git a/src/application/service.ts b/src/application/service.ts
index c686f77..3f221b4 100644
--- a/src/application/service.ts
+++ b/src/application/service.ts
@@ -187,6 +187,21 @@ export type T3ProjectApplicationService = {
   readonly resolveProject: (
     projectRef: string,
   ) => Effect.Effect<OrchestrationProjectShell, ApplicationError>;
+  readonly updateProject: (input: {
+    readonly projectRef: string;
+    readonly title?: string;
+    readonly workspaceRoot?: string;
+    readonly local: boolean;
+    readonly provider?: string;
+    readonly model?: string;
+    readonly options?: NonNullable<ModelSelection["options"]>;
+    readonly defaultModelSelection?: null;
+    readonly defaultThreadEnvironment?: "local" | "worktree" | null;
+    readonly favicon?: string | null;
+  }) => Effect.Effect<
+    { readonly dispatch: DispatchResult; readonly project: OrchestrationProjectShell },
+    ApplicationError
+  >;
   readonly deleteProject: (input: {
     readonly projectId: string;
     readonly force?: boolean;
diff --git a/src/cli/format/project.ts b/src/cli/format/project.ts
index 722e6db..199044e 100644
--- a/src/cli/format/project.ts
+++ b/src/cli/format/project.ts
@@ -24,6 +24,14 @@ export function formatProjectAddedHuman(project: OrchestrationProjectShell) {
   ])}`;
 }
 
+export function formatProjectUpdatedHuman(project: OrchestrationProjectShell) {
+  return `project updated\n${formatRecord([
+    { field: "title", value: project.title },
+    { field: "id", value: project.id },
+    { field: "path", value: project.workspaceRoot },
+  ])}`;
+}
+
 export function formatProjectDeletedHuman(input: {
   readonly projectId: string;
   readonly dispatch: { readonly sequence: number };
diff --git a/src/cli/project.ts b/src/cli/project.ts
index 33b1860..312d1be 100644
--- a/src/cli/project.ts
+++ b/src/cli/project.ts
@@ -6,6 +6,7 @@ import { extraArgsConfig } from "./extra-args.ts";
 import { formatFlag, projectPathFlag } from "./flags.ts";
 import { formatProjectAddedHuman, formatProjectsHuman } from "./format/project.ts";
 import { deleteProjectCommand } from "./projects/delete.ts";
+import { updateProjectCommand } from "./projects/update.ts";
 import { T3Application } from "../application/service.ts";
 import { CliRuntime } from "../cli/runtime/service.ts";
 import { loadT3CliEnv } from "../config/env/env.ts";
@@ -15,7 +16,7 @@ import { T3Output } from "./output/service.ts";
 export function createProjectCommand() {
   return Command.make("project").pipe(
     Command.withDescription("project commands"),
-    Command.withSubcommands([listCommand, addCommand, deleteProjectCommand]),
+    Command.withSubcommands([listCommand, addCommand, updateProjectCommand, deleteProjectCommand]),
   );
 }
 
diff --git a/src/cli/projects/update.test.ts b/src/cli/projects/update.test.ts
new file mode 100644
index 0000000..a40c1ad
--- /dev/null
+++ b/src/cli/projects/update.test.ts
@@ -0,0 +1,90 @@
+import "vite-plus/test/config";
+
+import * as Cause from "effect/Cause";
+import * as Effect from "effect/Effect";
+import * as Exit from "effect/Exit";
+import * as Layer from "effect/Layer";
+import * as NodeServices from "@effect/platform-node/NodeServices";
+import * as Option from "effect/Option";
+import { assert, describe, it } from "@effect/vitest";
+import { Command } from "effect/unstable/cli";
+import { fromPartial } from "@total-typescript/shoehorn";
+
+import { T3Application } from "../../application/service.ts";
+import { T3Config } from "../../config/config.ts";
+import { t3CliEnvConfigLayer } from "../../config/env/env.test-utils.ts";
+import * as CliRuntime from "../runtime/service.ts";
+import { T3Output } from "../output/service.ts";
+import { updateProjectCommand } from "./update.ts";
+
+const testLayer = Layer.mergeAll(
+  Layer.succeed(
+    T3Application,
+    fromPartial({ updateProject: () => Effect.die("updateProject should not be called") }),
+  ),
+  Layer.succeed(
+    T3Config,
+    fromPartial({
+      resolve: () =>
+        Effect.succeed({ url: "ws://localhost", token: "token", source: "config", local: true }),
+    }),
+  ),
+  Layer.succeed(T3Output, {
+    writeStdout: () => Effect.void,
+    writeStderr: () => Effect.void,
+    printJson: () => Effect.void,
+    printNdjson: () => Effect.void,
+    printInfo: () => Effect.void,
+  }),
+  NodeServices.layer,
+  CliRuntime.layer,
+  t3CliEnvConfigLayer("/tmp/t3cli-test"),
+);
+
+describe("updateProjectCommand", () => {
+  it.layer(testLayer)("validation", (t) => {
+    const run = Command.runWith(updateProjectCommand, { version: "0.0.0-test" });
+
+    t.effect("requires at least one update", () =>
+      expectError(run(["--project", "proj-1"]), "MissingUpdateFieldsError"),
+    );
+
+    t.effect("rejects a default model value with its clear flag", () =>
+      expectError(
+        run(["--project", "proj-1", "--model", "gpt-5", "--clear-default-model"]),
+        "ConflictingUpdateFlagsError",
+      ),
+    );
+
+    t.effect("rejects a favicon value with its clear flag", () =>
+      expectError(
+        run(["--project", "proj-1", "--favicon", "icon.png", "--clear-favicon"]),
+        "ConflictingUpdateFlagsError",
+      ),
+    );
+
+    t.effect("rejects a thread environment value with its clear flag", () =>
+      expectError(
+        run(["--project", "proj-1", "--thread-env", "local", "--clear-thread-env"]),
+        "ConflictingUpdateFlagsError",
+      ),
+    );
+  });
+});
+
+function expectError<R>(
+  effect: Effect.Effect<unknown, unknown, R>,
+  expectedTag: string,
+) {
+  return Effect.gen(function* () {
+    const exit = yield* effect.pipe(Effect.exit);
+    assert.isTrue(Exit.isFailure(exit));
+    if (Exit.isFailure(exit)) {
+      const error = Cause.findErrorOption(exit.cause);
+      assert.isTrue(Option.isSome(error));
+      if (Option.isSome(error)) {
+        assert.equal((error.value as { readonly _tag?: string })._tag, expectedTag);
+      }
+    }
+  });
+}
diff --git a/src/cli/projects/update.ts b/src/cli/projects/update.ts
new file mode 100644
index 0000000..2b83418
--- /dev/null
+++ b/src/cli/projects/update.ts
@@ -0,0 +1,105 @@
+import * as Effect from "effect/Effect";
+import * as Option from "effect/Option";
+import { Command, Flag } from "effect/unstable/cli";
+
+import { T3Application } from "../../application/service.ts";
+import { CliRuntime } from "../runtime/service.ts";
+import { T3Config } from "../../config/config.ts";
+import { loadT3CliEnv } from "../../config/env/env.ts";
+import { extraArgsConfig } from "../extra-args.ts";
+import { ConflictingUpdateFlagsError, MissingUpdateFieldsError } from "../error.ts";
+import { formatFlag, modelFlags, projectFlag } from "../flags.ts";
+import { formatProjectUpdatedHuman } from "../format/project.ts";
+import { resolveOutputFormat } from "../format/output.ts";
+import { buildModelOptions } from "../model-options.ts";
+import { T3Output } from "../output/service.ts";
+import { requireCommandProjectRef } from "../require.ts";
+
+export const updateProjectCommand = Command.make(
+  "update",
+  {
+    project: projectFlag,
+    title: Flag.string("title").pipe(Flag.optional),
+    workspaceRoot: Flag.string("workspace-root").pipe(Flag.optional),
+    provider: Flag.string("provider").pipe(Flag.optional),
+    model: Flag.string("model").pipe(Flag.optional),
+    ...modelFlags,
+    clearDefaultModel: Flag.boolean("clear-default-model").pipe(Flag.optional),
+    threadEnv: Flag.choice("thread-env", ["local", "worktree"] as const).pipe(Flag.optional),
+    clearThreadEnv: Flag.boolean("clear-thread-env").pipe(Flag.optional),
+    favicon: Flag.string("favicon").pipe(Flag.optional),
+    clearFavicon: Flag.boolean("clear-favicon").pipe(Flag.optional),
+    format: formatFlag,
+    ...extraArgsConfig,
+  },
+  (flags) =>
+    Effect.gen(function* () {
+      const title = Option.getOrUndefined(flags.title);
+      const workspaceRoot = Option.getOrUndefined(flags.workspaceRoot);
+      const provider = Option.getOrUndefined(flags.provider);
+      const model = Option.getOrUndefined(flags.model);
+      const threadEnv = Option.getOrUndefined(flags.threadEnv);
+      const favicon = Option.getOrUndefined(flags.favicon);
+      const clearDefaultModel = Option.getOrUndefined(flags.clearDefaultModel) === true;
+      const clearThreadEnv = Option.getOrUndefined(flags.clearThreadEnv) === true;
+      const clearFavicon = Option.getOrUndefined(flags.clearFavicon) === true;
+      const options = buildModelOptions(flags);
+      const hasModel = provider !== undefined || model !== undefined || options.length > 0;
+
+      if (hasModel && clearDefaultModel) {
+        return yield* conflict("model flags and --clear-default-model are mutually exclusive");
+      }
+      if (threadEnv !== undefined && clearThreadEnv) {
+        return yield* conflict("--thread-env and --clear-thread-env are mutually exclusive");
+      }
+      if (favicon !== undefined && clearFavicon) {
+        return yield* conflict("--favicon and --clear-favicon are mutually exclusive");
+      }
+      if (
+        title === undefined &&
+        workspaceRoot === undefined &&
+        !hasModel &&
+        !clearDefaultModel &&
+        threadEnv === undefined &&
+        !clearThreadEnv &&
+        favicon === undefined &&
+        !clearFavicon
+      ) {
+        return yield* Effect.fail(
+          new MissingUpdateFieldsError({
+            message: "at least one project metadata update field is required",
+          }),
+        );
+      }
+
+      const application = yield* T3Application;
+      const config = yield* T3Config;
+      const runtime = yield* CliRuntime;
+      const env = yield* loadT3CliEnv;
+      const output = yield* T3Output;
+      const result = yield* application.updateProject({
+        projectRef: yield* requireCommandProjectRef({ project: flags.project }),
+        local: (yield* config.resolve()).local,
+        ...(title !== undefined ? { title } : {}),
+        ...(workspaceRoot !== undefined ? { workspaceRoot } : {}),
+        ...(provider !== undefined ? { provider } : {}),
+        ...(model !== undefined ? { model } : {}),
+        ...(options.length > 0 ? { options } : {}),
+        ...(clearDefaultModel ? { defaultModelSelection: null } : {}),
+        ...(clearThreadEnv
+          ? { defaultThreadEnvironment: null }
+          : threadEnv !== undefined
+            ? { defaultThreadEnvironment: threadEnv }
+            : {}),
+        ...(clearFavicon ? { favicon: null } : favicon !== undefined ? { favicon } : {}),
+      });
+      if (resolveOutputFormat(flags.format, runtime, env, "json") === "json") {
+        return yield* output.printJson(result.project);
+      }
+      return yield* output.printInfo(formatProjectUpdatedHuman(result.project));
+    }),
+).pipe(Command.withDescription("update project metadata"));
+
+function conflict(message: string) {
+  return Effect.fail(new ConflictingUpdateFlagsError({ message }));
+}
diff --git a/src/domain/error.ts b/src/domain/error.ts
index d901836..8a60152 100644
--- a/src/domain/error.ts
+++ b/src/domain/error.ts
@@ -72,6 +72,11 @@ export class ProjectActionValidationError extends Schema.TaggedErrorClass<Projec
   },
 ) {}
 
+export class ProjectUpdateValidationError extends Schema.TaggedErrorClass<ProjectUpdateValidationError>()(
+  "ProjectUpdateValidationError",
+  { message: Schema.String, projectId: Schema.String },
+) {}
+
 export type DomainError =
   | ProjectLookupError
   | ModelSelectionError
@@ -81,4 +86,5 @@ export type DomainError =
   | ProjectCreateVisibilityError
   | TerminalLookupError
   | ProjectActionLookupError
-  | ProjectActionValidationError;
+  | ProjectActionValidationError
+  | ProjectUpdateValidationError;