diff --git a/packages/coding-agent/src/core/agent-session.ts b/packages/coding-agent/src/core/agent-session.ts
index 111adcd2c..4517dc318 100644
--- a/packages/coding-agent/src/core/agent-session.ts
+++ b/packages/coding-agent/src/core/agent-session.ts
@@ -2057,6 +2057,20 @@ export class AgentSession {
 			: undefined;
 	}
 
+	private _refreshCurrentModelFromRegistry(): void {
+		const currentModel = this.model;
+		if (!currentModel) {
+			return;
+		}
+
+		const refreshedModel = this._modelRegistry.find(currentModel.provider, currentModel.id);
+		if (!refreshedModel || refreshedModel === currentModel) {
+			return;
+		}
+
+		this.agent.setModel(refreshedModel);
+	}
+
 	private _bindExtensionCore(runner: ExtensionRunner): void {
 		const normalizeLocation = (source: string): SlashCommandLocation | undefined => {
 			if (source === "user" || source === "project" || source === "path") {
@@ -2165,6 +2179,16 @@ export class AgentSession {
 				},
 				getSystemPrompt: () => this.systemPrompt,
 			},
+			{
+				registerProvider: (name, config) => {
+					this._modelRegistry.registerProvider(name, config);
+					this._refreshCurrentModelFromRegistry();
+				},
+				unregisterProvider: (name) => {
+					this._modelRegistry.unregisterProvider(name);
+					this._refreshCurrentModelFromRegistry();
+				},
+			},
 		);
 	}
 
diff --git a/packages/coding-agent/src/core/extensions/runner.ts b/packages/coding-agent/src/core/extensions/runner.ts
index 05f2d786f..65234bb4a 100644
--- a/packages/coding-agent/src/core/extensions/runner.ts
+++ b/packages/coding-agent/src/core/extensions/runner.ts
@@ -34,6 +34,7 @@ import type {
 	InputEventResult,
 	InputSource,
 	MessageRenderer,
+	ProviderConfig,
 	RegisteredCommand,
 	RegisteredTool,
 	ResourcesDiscoverEvent,
@@ -235,7 +236,14 @@ export class ExtensionRunner {
 		this.modelRegistry = modelRegistry;
 	}
 
-	bindCore(actions: ExtensionActions, contextActions: ExtensionContextActions): void {
+	bindCore(
+		actions: ExtensionActions,
+		contextActions: ExtensionContextActions,
+		providerActions?: {
+			registerProvider?: (name: string, config: ProviderConfig) => void;
+			unregisterProvider?: (name: string) => void;
+		},
+	): void {
 		// Copy actions into the shared runtime (all extension APIs reference this)
 		this.runtime.sendMessage = actions.sendMessage;
 		this.runtime.sendUserMessage = actions.sendUserMessage;
@@ -264,14 +272,30 @@ export class ExtensionRunner {
 
 		// Flush provider registrations queued during extension loading
 		for (const { name, config } of this.runtime.pendingProviderRegistrations) {
-			this.modelRegistry.registerProvider(name, config);
+			if (providerActions?.registerProvider) {
+				providerActions.registerProvider(name, config);
+			} else {
+				this.modelRegistry.registerProvider(name, config);
+			}
 		}
 		this.runtime.pendingProviderRegistrations = [];
 
 		// From this point on, provider registration/unregistration takes effect immediately
 		// without requiring a /reload.
-		this.runtime.registerProvider = (name, config) => this.modelRegistry.registerProvider(name, config);
-		this.runtime.unregisterProvider = (name) => this.modelRegistry.unregisterProvider(name);
+		this.runtime.registerProvider = (name, config) => {
+			if (providerActions?.registerProvider) {
+				providerActions.registerProvider(name, config);
+				return;
+			}
+			this.modelRegistry.registerProvider(name, config);
+		};
+		this.runtime.unregisterProvider = (name) => {
+			if (providerActions?.unregisterProvider) {
+				providerActions.unregisterProvider(name);
+				return;
+			}
+			this.modelRegistry.unregisterProvider(name);
+		};
 	}
 
 	bindCommandContext(actions?: ExtensionCommandContextActions): void {
diff --git a/packages/coding-agent/test/agent-session-dynamic-provider.test.ts b/packages/coding-agent/test/agent-session-dynamic-provider.test.ts
new file mode 100644
index 000000000..6c3b81352
--- /dev/null
+++ b/packages/coding-agent/test/agent-session-dynamic-provider.test.ts
@@ -0,0 +1,117 @@
+import { existsSync, mkdirSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { getModel } from "@mariozechner/pi-ai";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { AuthStorage } from "../src/core/auth-storage.js";
+import { DefaultResourceLoader } from "../src/core/resource-loader.js";
+import type { ExtensionFactory } from "../src/core/sdk.js";
+import { createAgentSession } from "../src/core/sdk.js";
+import { SessionManager } from "../src/core/session-manager.js";
+import { SettingsManager } from "../src/core/settings-manager.js";
+
+describe("AgentSession dynamic provider registration", () => {
+	let tempDir: string;
+	let agentDir: string;
+
+	beforeEach(() => {
+		tempDir = join(tmpdir(), `pi-dynamic-provider-test-${Date.now()}-${Math.random().toString(36).slice(2)}`);
+		agentDir = join(tempDir, "agent");
+		mkdirSync(agentDir, { recursive: true });
+	});
+
+	afterEach(() => {
+		if (tempDir && existsSync(tempDir)) {
+			rmSync(tempDir, { recursive: true, force: true });
+		}
+	});
+
+	async function createSession(extensionFactories: ExtensionFactory[]) {
+		const settingsManager = SettingsManager.create(tempDir, agentDir);
+		const sessionManager = SessionManager.inMemory();
+		const authStorage = AuthStorage.create(join(agentDir, "auth.json"));
+		authStorage.setRuntimeApiKey("anthropic", "test-key");
+		const resourceLoader = new DefaultResourceLoader({
+			cwd: tempDir,
+			agentDir,
+			settingsManager,
+			extensionFactories,
+		});
+		await resourceLoader.reload();
+
+		const { session } = await createAgentSession({
+			cwd: tempDir,
+			agentDir,
+			model: getModel("anthropic", "claude-sonnet-4-5")!,
+			settingsManager,
+			sessionManager,
+			authStorage,
+			resourceLoader,
+		});
+
+		return session;
+	}
+
+	async function capturePromptBaseUrl(
+		session: Awaited<ReturnType<typeof createSession>>,
+	): Promise<string | undefined> {
+		let baseUrl: string | undefined;
+		session.agent.streamFn = async (model) => {
+			baseUrl = model.baseUrl;
+			throw new Error("stop");
+		};
+		await session.prompt("hello");
+		return baseUrl;
+	}
+
+	it("applies top-level registerProvider overrides to the active model", async () => {
+		const session = await createSession([
+			(pi) => {
+				pi.registerProvider("anthropic", { baseUrl: "http://localhost:8080/top-level" });
+			},
+		]);
+
+		expect(session.model?.baseUrl).toBe("http://localhost:8080/top-level");
+		expect(await capturePromptBaseUrl(session)).toBe("http://localhost:8080/top-level");
+
+		session.dispose();
+	});
+
+	it("applies session_start registerProvider overrides to the active model", async () => {
+		const session = await createSession([
+			(pi) => {
+				pi.on("session_start", () => {
+					pi.registerProvider("anthropic", { baseUrl: "http://localhost:8080/session-start" });
+				});
+			},
+		]);
+
+		await session.bindExtensions({});
+
+		expect(session.model?.baseUrl).toBe("http://localhost:8080/session-start");
+		expect(await capturePromptBaseUrl(session)).toBe("http://localhost:8080/session-start");
+
+		session.dispose();
+	});
+
+	it("applies command-time registerProvider overrides without reload", async () => {
+		const session = await createSession([
+			(pi) => {
+				pi.registerCommand("use-proxy", {
+					description: "Use proxy",
+					handler: async () => {
+						pi.registerProvider("anthropic", { baseUrl: "http://localhost:8080/command" });
+					},
+				});
+			},
+		]);
+
+		await session.bindExtensions({});
+		await session.prompt("/use-proxy");
+
+		expect(session.model?.baseUrl).toBe("http://localhost:8080/command");
+		expect(await capturePromptBaseUrl(session)).toBe("http://localhost:8080/command");
+
+		session.dispose();
+	});
+});