diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index 64c3c57ae..2fe913737 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -19,6 +19,8 @@
 
 ### Fixed
 
+- Fixed `models.yml` schema validation failures being treated as valid config data, so invalid custom provider files now surface a warning instead of silently dropping all custom providers. ([#4305](https://github.com/can1357/oh-my-pi/issues/4305))
+
 - Fixed stuttering/latency in speech by running synthesis chunks through the player gaplessly
 - Fixed race condition causing EPIPE errors and broken pipes during speech playback
 - Fixed interrupted speech audio by ensuring segments queue and drain in order
diff --git a/packages/coding-agent/src/cli/models-cli.ts b/packages/coding-agent/src/cli/models-cli.ts
index 5bc862ae0..ca43238ec 100644
--- a/packages/coding-agent/src/cli/models-cli.ts
+++ b/packages/coding-agent/src/cli/models-cli.ts
@@ -84,6 +84,14 @@ function writeLine(line = ""): void {
 	process.stdout.write(`${line}\n`);
 }
 
+function writeModelsConfigError(error: Error): void {
+	writeLine(chalk.yellow("Warning: models.yml validation failed — custom providers disabled"));
+	for (const line of error.message.split("\n")) {
+		writeLine(`  ${line}`);
+	}
+	writeLine();
+}
+
 function formatLimit(n: number | null): string {
 	return n === null ? "-" : formatNumber(n);
 }
@@ -187,12 +195,23 @@ function renderProviderModels(
 		}
 	}
 
+	const configError = modelRegistry.getError();
+
 	if (json) {
+		if (configError) {
+			process.stderr.write(
+				`Warning: models.yml validation failed — custom providers disabled\n${configError.message}\n`,
+			);
+		}
 		const output: ModelsJson = { models: filtered.slice().sort(byProviderThenId).map(toModelJson) };
 		writeLine(JSON.stringify(output));
 		return;
 	}
 
+	if (configError) {
+		writeModelsConfigError(configError);
+	}
+
 	if (available.length === 0) {
 		writeLine("No models available. Set API keys in environment variables.");
 		return;
diff --git a/packages/coding-agent/src/config/config-file.ts b/packages/coding-agent/src/config/config-file.ts
index 018d25c8f..5c73fc9d9 100644
--- a/packages/coding-agent/src/config/config-file.ts
+++ b/packages/coding-agent/src/config/config-file.ts
@@ -1,7 +1,7 @@
 import * as fs from "node:fs";
 import * as path from "node:path";
 import { getAgentDir, isEnoent, logger } from "@oh-my-pi/pi-utils";
-import type { Type } from "arktype";
+import { ArkErrors, type Type } from "arktype";
 import { JSONC, YAML } from "bun";
 
 /** Minimal subset of the AJV ConfigSchemaError shape this module actually relies on. */
@@ -220,11 +220,11 @@ export class ConfigFile<T> implements IConfigFile<T> {
 			}
 
 			const checked = this.schema(parsed);
-			if (checked instanceof Error) {
-				const schemaErrors: ConfigSchemaError[] = [];
-				// arktype errors are Error instances with a message property
-				// Extract the error message as a single schema error
-				schemaErrors.push({ instancePath: "root", message: checked.message });
+			if (checked instanceof ArkErrors) {
+				const schemaErrors: ConfigSchemaError[] = checked.map(error => ({
+					instancePath: error.path.length === 0 ? "root" : error.path.join("."),
+					message: error.problem,
+				}));
 				const error = new ConfigError(this.id, schemaErrors);
 				logger.warn("Failed to parse config file", { path: this.path(), error });
 				return this.#storeCache({ error, status: "error" });
diff --git a/packages/coding-agent/src/main.ts b/packages/coding-agent/src/main.ts
index a863e9366..245e10434 100644
--- a/packages/coding-agent/src/main.ts
+++ b/packages/coding-agent/src/main.ts
@@ -1383,6 +1383,9 @@ export async function runRootCommand(
 		}
 
 		if (!isInteractive && !session.model) {
+			if (modelRegistryError) {
+				process.stderr.write(`${chalk.red(modelRegistryError.message)}\n\n`);
+			}
 			if (modelFallbackMessage) {
 				process.stderr.write(`${chalk.red(modelFallbackMessage)}\n`);
 			} else {
diff --git a/packages/coding-agent/test/issue-905-repro.test.ts b/packages/coding-agent/test/issue-905-repro.test.ts
index 63da70f65..ff665d311 100644
--- a/packages/coding-agent/test/issue-905-repro.test.ts
+++ b/packages/coding-agent/test/issue-905-repro.test.ts
@@ -85,3 +85,57 @@ test("omp models surfaces extension-registered providers (issue #905)", async ()
 		authStorage.close();
 	}
 });
+
+test("omp models prints invalid models.yml schema errors before listing output", async () => {
+	const modelsPath = tmp.join("invalid-models.yml");
+	await fs.writeFile(
+		modelsPath,
+		`providers:
+  myprovider:
+    baseUrl: http://localhost:8000/v1
+    api: openai-completions
+    auth: none
+    compat:
+      thinkingFormat: deepseek
+    models:
+      - id: my-model
+        name: My Model
+        reasoning: false
+        input: [text]
+        cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 }
+        contextWindow: 8192
+        maxTokens: 4096
+`,
+	);
+
+	const authStorage = await AuthStorage.create(":memory:");
+	try {
+		const modelRegistry = new ModelRegistry(authStorage, modelsPath);
+
+		const captured: string[] = [];
+		const originalWrite = process.stdout.write;
+		Reflect.set(process.stdout, "write", (chunk: string | Uint8Array) => {
+			captured.push(typeof chunk === "string" ? chunk : Buffer.from(chunk).toString("utf8"));
+			return true;
+		});
+
+		try {
+			await runModelsListing({
+				modelRegistry,
+				cwd: tmp.path(),
+				action: "ls",
+				pattern: "myprovider",
+				disableExtensionDiscovery: true,
+			});
+		} finally {
+			process.stdout.write = originalWrite;
+		}
+
+		const output = captured.join("");
+		expect(output).toContain("Warning: models.yml validation failed — custom providers disabled");
+		expect(output).toContain("providers.myprovider.compat.thinkingFormat");
+		expect(output).toContain("deepseek");
+	} finally {
+		authStorage.close();
+	}
+});
diff --git a/packages/coding-agent/test/model-registry.test.ts b/packages/coding-agent/test/model-registry.test.ts
index 58f89aa6e..643069d30 100644
--- a/packages/coding-agent/test/model-registry.test.ts
+++ b/packages/coding-agent/test/model-registry.test.ts
@@ -1230,6 +1230,36 @@ describe("ModelRegistry", () => {
 			expect(nonexistent.getError()).toBeUndefined();
 		});
 
+		test("invalid models config exposes schema errors instead of silently dropping providers", () => {
+			writeRawModelsJson({
+				myprovider: {
+					baseUrl: "http://localhost:8000/v1",
+					api: "openai-completions",
+					auth: "none",
+					compat: { thinkingFormat: "deepseek" },
+					models: [
+						{
+							id: "my-model",
+							name: "My Model",
+							reasoning: false,
+							input: ["text"],
+							cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+							contextWindow: 8192,
+							maxTokens: 4096,
+						},
+					],
+				},
+			});
+
+			const invalid = new ModelRegistry(authStorage, modelsJsonPath);
+			const error = invalid.getError();
+
+			expect(error?.message).toContain("Failed to load config file models, Schema error");
+			expect(error?.message).toContain("providers.myprovider.compat.thinkingFormat");
+			expect(error?.message).toContain("deepseek");
+			expect(invalid.find("myprovider", "my-model")).toBeUndefined();
+		});
+
 		test("model override can change cost fields partially", () => {
 			const sonnet = getModelsForProvider(costPartial, "openrouter").find(m => m.id === "anthropic/claude-sonnet-4");
 			// Input cost should be overridden