feat(coding-agent): surfaced active model in system prompt

- Rendered the active model identifier into the project prompt.
- Rebuilt the cached base prompt on model switch to avoid staleness.

packages/coding-agent/CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Added
 
+- Added the active model identifier (`provider/id`) to the system prompt's `<workstation>` block so the agent knows which model it is running as. Gated by the new `includeModelInPrompt` setting (default on); the base prompt is rebuilt on a mid-session model switch so the surfaced identifier stays current.
 - Added `OLLAMA_HOST` support for implicit local Ollama discovery when `OLLAMA_BASE_URL` is unset, so OMP picks up the same host setting used by Ollama.
 - Added `OLLAMA_CONTEXT_LENGTH` as a positive-integer context-window override for implicit local Ollama discovery, so users can correct OMP context budgeting without writing per-model overrides.
 

packages/coding-agent/src/config/settings-schema.ts

@@ -722,6 +722,16 @@ export const SETTINGS_SCHEMA = {
 		},
 	},
 
+	includeModelInPrompt: {
+		type: "boolean",
+		default: true,
+		ui: {
+			tab: "model",
+			label: "Include Model In Prompt",
+			description: "Surface the active model identifier in the system prompt so the agent knows which model it is",
+		},
+	},
+
 	// Sampling
 	temperature: {
 		type: "number",

packages/coding-agent/src/prompts/system/project-prompt.md

@@ -3,6 +3,7 @@ PROJECT
 
 <workstation>
 {{#list environment prefix="- " join="\n"}}{{label}}: {{value}}{{/list}}
+{{#if model}}- Model: {{model}}{{/if}}
 </workstation>
 
 {{#if contextFiles.length}}

packages/coding-agent/src/sdk.ts

@@ -1773,6 +1773,7 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 				secretsEnabled,
 				workspaceTree: workspaceTreePromise,
 				memoryRootEnabled: memoryBackend.id === "local",
+				model: settings.get("includeModelInPrompt") ? getActiveModelString() : undefined,
 			});
 
 			if (options.systemPrompt === undefined) {

packages/coding-agent/src/session/agent-session.ts

@@ -960,6 +960,13 @@ export class AgentSession {
 	 * the dominant cause of prompt-cache invalidation in long sessions.
 	 */
 	#lastAppliedToolSignature: string | undefined;
+	/**
+	 * Model identifier (`provider/id`) currently rendered into `#baseSystemPrompt`.
+	 * The prompt surfaces the active model to the agent, so a model switch must
+	 * trigger a rebuild. Compared against the live model after every model change
+	 * to decide whether the cached prompt is stale.
+	 */
+	#promptModelKey: string | undefined;
 	#mcpDiscoveryEnabled = false;
 	#discoverableMCPTools = new Map<string, DiscoverableTool>();
 	#selectedMCPToolNames = new Set<string>();
@@ -1173,6 +1180,7 @@ export class AgentSession {
 		this.#getMcpServerInstructions = config.getMcpServerInstructions;
 		this.#reloadSshTool = config.reloadSshTool;
 		this.#baseSystemPrompt = this.agent.state.systemPrompt;
+		this.#promptModelKey = this.#currentPromptModelKey();
 		this.#mcpDiscoveryEnabled = config.mcpDiscoveryEnabled ?? false;
 		this.#setDiscoverableMCPTools(this.#collectDiscoverableMCPToolsFromRegistry());
 		this.#selectedMCPToolNames = new Set(config.initialSelectedMCPToolNames ?? []);
@@ -3264,9 +3272,21 @@ export class AgentSession {
 		return resolveEditMode(this.#getEditModeSession());
 	}
 
-	async #syncEditToolModeAfterModelChange(previousEditMode: EditMode): Promise<void> {
+	/**
+	 * Model key (`provider/id`) currently surfaced in the system prompt, or
+	 * undefined when the model is unset or `includeModelInPrompt` is disabled.
+	 */
+	#currentPromptModelKey(): string | undefined {
+		if (!this.settings.get("includeModelInPrompt")) return undefined;
+		return this.model ? formatModelString(this.model) : undefined;
+	}
+
+	async #syncAfterModelChange(previousEditMode: EditMode): Promise<void> {
 		const currentEditMode = this.#resolveActiveEditMode();
-		if (previousEditMode !== currentEditMode && this.getActiveToolNames().includes("edit")) {
+		const editModeChanged = previousEditMode !== currentEditMode && this.getActiveToolNames().includes("edit");
+		// The system prompt may surface the active model; a switch makes the cached prompt stale.
+		const modelChanged = this.#currentPromptModelKey() !== this.#promptModelKey;
+		if (editModeChanged || modelChanged) {
 			await this.refreshBaseSystemPrompt();
 		}
 	}
@@ -3551,6 +3571,7 @@ export class AgentSession {
 				this.#baseSystemPrompt = built.systemPrompt;
 				this.agent.setSystemPrompt(this.#baseSystemPrompt);
 				this.#lastAppliedToolSignature = signature;
+				this.#promptModelKey = this.#currentPromptModelKey();
 			}
 		}
 		if (options?.persistMCPSelection !== false) {
@@ -3633,6 +3654,7 @@ export class AgentSession {
 		const built = await this.#rebuildSystemPrompt(activeToolNames, this.#toolRegistry);
 		this.#baseSystemPrompt = built.systemPrompt;
 		this.agent.setSystemPrompt(this.#baseSystemPrompt);
+		this.#promptModelKey = this.#currentPromptModelKey();
 		// Refresh the cached signature so a subsequent `#applyActiveToolsByName` with
 		// the same tool set does not re-rebuild on top of the explicit refresh we
 		// just performed (and conversely, a different set forces a fresh rebuild).
@@ -3692,7 +3714,7 @@ export class AgentSession {
 	 * closure-captured ones cannot change at runtime regardless of skip behavior.
 	 * For everything else, callers must explicitly call `refreshBaseSystemPrompt()`
 	 * after side-effecting changes; see e.g. the memory hooks and
-	 * `#syncEditToolModeAfterModelChange`.
+	 * `#syncAfterModelChange`.
 	 *
 	 * The current calendar date IS covered (appended as a segment) because
 	 * `buildSystemPrompt` injects it into the prompt body (`Today is '{{date}}'`).
@@ -5284,7 +5306,7 @@ export class AgentSession {
 		// Re-apply thinking for the newly selected model. Prefer the model's
 		// configured defaultLevel; otherwise preserve the current level (or auto).
 		this.#reapplyThinkingLevel(model.thinking?.defaultLevel);
-		await this.#syncEditToolModeAfterModelChange(previousEditMode);
+		await this.#syncAfterModelChange(previousEditMode);
 	}
 
 	/**
@@ -5318,7 +5340,7 @@ export class AgentSession {
 		} else {
 			this.#reapplyThinkingLevel(model.thinking?.defaultLevel);
 		}
-		await this.#syncEditToolModeAfterModelChange(previousEditMode);
+		await this.#syncAfterModelChange(previousEditMode);
 	}
 
 	/**
@@ -5462,7 +5484,7 @@ export class AgentSession {
 
 		// Apply the scoped model's configured thinking level, preserving auto.
 		this.setThinkingLevel(this.#autoThinking ? AUTO_THINKING : next.thinkingLevel);
-		await this.#syncEditToolModeAfterModelChange(previousEditMode);
+		await this.#syncAfterModelChange(previousEditMode);
 
 		return { model: next.model, thinkingLevel: this.thinkingLevel, isScoped: true };
 	}
@@ -5491,7 +5513,7 @@ export class AgentSession {
 		this.settings.getStorage()?.recordModelUsage(`${nextModel.provider}/${nextModel.id}`);
 		// Re-apply the current thinking level (or auto) for the newly selected model
 		this.#reapplyThinkingLevel();
-		await this.#syncEditToolModeAfterModelChange(previousEditMode);
+		await this.#syncAfterModelChange(previousEditMode);
 
 		return { model: nextModel, thinkingLevel: this.thinkingLevel, isScoped: false };
 	}

packages/coding-agent/src/system-prompt.ts

@@ -363,6 +363,8 @@ export interface BuildSystemPromptOptions {
 	workspaceTree?: WorkspaceTree | Promise<WorkspaceTree>;
 	/** Whether the local memory://root summary is active. */
 	memoryRootEnabled?: boolean;
+	/** Active model identifier (e.g. "anthropic/claude-opus-4") surfaced to the agent. */
+	model?: string;
 }
 
 /** Result of building provider-facing system prompt messages. */
@@ -396,6 +398,7 @@ export async function buildSystemPrompt(options: BuildSystemPromptOptions = {}):
 		secretsEnabled = false,
 		workspaceTree: providedWorkspaceTree,
 		memoryRootEnabled = false,
+		model,
 	} = options;
 	const resolvedCwd = cwd ?? getProjectDir();
 
@@ -566,6 +569,7 @@ export async function buildSystemPrompt(options: BuildSystemPromptOptions = {}):
 		date,
 		dateTime,
 		cwd: promptCwd,
+		model: model ?? "",
 		intentTracing: !!intentField,
 		intentField: intentField ?? "",
 		mcpDiscoveryMode,

packages/coding-agent/test/system-prompt-model.test.ts

@@ -0,0 +1,154 @@
+import { afterEach, beforeEach, describe, expect, it } from "bun:test";
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+import { Agent } from "@oh-my-pi/pi-agent-core";
+import type { Model } from "@oh-my-pi/pi-ai";
+import { ModelRegistry } from "@oh-my-pi/pi-coding-agent/config/model-registry";
+import { Settings } from "@oh-my-pi/pi-coding-agent/config/settings";
+import { AgentSession } from "@oh-my-pi/pi-coding-agent/session/agent-session";
+import { AuthStorage } from "@oh-my-pi/pi-coding-agent/session/auth-storage";
+import { SessionManager } from "@oh-my-pi/pi-coding-agent/session/session-manager";
+import { buildSystemPrompt } from "@oh-my-pi/pi-coding-agent/system-prompt";
+import { cleanupTempHome } from "./helpers/temp-home-cleanup";
+
+const EMPTY_TREE = {
+	rootPath: "",
+	rendered: "",
+	truncated: false,
+	totalLines: 0,
+	agentsMdFiles: [],
+};
+
+describe("system prompt model identifier", () => {
+	let tempDir = "";
+	let tempHomeDir = "";
+	let originalHome: string | undefined;
+
+	beforeEach(() => {
+		tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "pi-prompt-model-"));
+		tempHomeDir = fs.mkdtempSync(path.join(os.tmpdir(), "pi-prompt-model-home-"));
+		originalHome = process.env.HOME;
+		process.env.HOME = tempHomeDir;
+	});
+
+	afterEach(cleanupTempHome(() => ({ tempDir, tempHomeDir, originalHome })));
+
+	it("renders the model identifier into the workstation block when provided", async () => {
+		const { systemPrompt } = await buildSystemPrompt({
+			cwd: tempDir,
+			contextFiles: [],
+			skills: [],
+			rules: [],
+			toolNames: [],
+			workspaceTree: { ...EMPTY_TREE, rootPath: tempDir },
+			model: "anthropic/claude-opus-4",
+		});
+
+		expect(systemPrompt.join("\n\n")).toContain("Model: anthropic/claude-opus-4");
+	});
+
+	it("omits the model line when no model is provided", async () => {
+		const { systemPrompt } = await buildSystemPrompt({
+			cwd: tempDir,
+			contextFiles: [],
+			skills: [],
+			rules: [],
+			toolNames: [],
+			workspaceTree: { ...EMPTY_TREE, rootPath: tempDir },
+		});
+
+		expect(systemPrompt.join("\n\n")).not.toContain("Model:");
+	});
+});
+
+describe("AgentSession model-change prompt refresh", () => {
+	let authStorage: AuthStorage;
+	let modelRegistry: ModelRegistry;
+	let tempDir: string;
+	let session: AgentSession | undefined;
+
+	beforeEach(async () => {
+		tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "pi-prompt-model-session-"));
+		authStorage = await AuthStorage.create(path.join(tempDir, "auth.db"));
+		modelRegistry = new ModelRegistry(authStorage);
+	});
+
+	afterEach(async () => {
+		if (session) {
+			await session.dispose();
+			session = undefined;
+		}
+		authStorage.close();
+		fs.rmSync(tempDir, { recursive: true, force: true });
+	});
+
+	function pickTwoModels(): [Model, Model] {
+		const all = modelRegistry.getAll();
+		const first = all[0];
+		const second = all.find(m => m.provider !== first.provider || m.id !== first.id);
+		if (!first || !second) throw new Error("Expected at least two distinct models in the registry");
+		return [first, second];
+	}
+
+	function newSession(
+		model: Model,
+		settings: Settings,
+		rebuild: () => Promise<{ systemPrompt: string[] }>,
+	): AgentSession {
+		const agent = new Agent({
+			getApiKey: () => "test-key",
+			initialState: { model, systemPrompt: ["initial"], tools: [], messages: [] },
+		});
+		const created = new AgentSession({
+			agent,
+			sessionManager: SessionManager.inMemory(),
+			settings,
+			modelRegistry,
+			toolRegistry: new Map(),
+			rebuildSystemPrompt: async () => rebuild(),
+		});
+		return created;
+	}
+
+	it("rebuilds the prompt with the new model when includeModelInPrompt is enabled", async () => {
+		const [modelA, modelB] = pickTwoModels();
+		authStorage.setRuntimeApiKey(modelA.provider, "key-a");
+		authStorage.setRuntimeApiKey(modelB.provider, "key-b");
+
+		let rebuildCount = 0;
+		session = newSession(modelA, Settings.isolated({ "compaction.enabled": false }), async () => {
+			rebuildCount++;
+			const active = session?.model;
+			return { systemPrompt: [`model:${active ? `${active.provider}/${active.id}` : ""}`] };
+		});
+
+		await session.setModel(modelB);
+		expect(rebuildCount).toBe(1);
+		expect(session.agent.state.systemPrompt).toEqual([`model:${modelB.provider}/${modelB.id}`]);
+
+		// Re-selecting the same model leaves the rendered model unchanged → no rebuild.
+		await session.setModel(modelB);
+		expect(rebuildCount).toBe(1);
+	});
+
+	it("does not rebuild on model change when includeModelInPrompt is disabled", async () => {
+		const [modelA, modelB] = pickTwoModels();
+		authStorage.setRuntimeApiKey(modelA.provider, "key-a");
+		authStorage.setRuntimeApiKey(modelB.provider, "key-b");
+
+		let rebuildCount = 0;
+		session = newSession(
+			modelA,
+			Settings.isolated({ "compaction.enabled": false, includeModelInPrompt: false }),
+			async () => {
+				rebuildCount++;
+				return { systemPrompt: ["unchanged"] };
+			},
+		);
+
+		await session.setModel(modelB);
+		expect(rebuildCount).toBe(0);
+		expect(session.agent.state.systemPrompt).toEqual(["initial"]);
+	});
+});