AI Coding Agents Still Write Your SDK's Old API — SDKProof Measures the Gap with Type-Checking

AI coding agents still write your SDK’s old API — so I built a type-checker to measure it

Developer Kalpit Rathore built SDKProof to quantify how often AI assistants generate broken code against current library APIs. Across three major SDKs—Prisma 7, Vercel AI SDK 7, and Zod 4—the tool found that models score between 80 and 90 out of 100 on realistic tasks, failing primarily due to renamed or removed options from recent major releases.

Why This Matters

Large language models are frozen at their training cutoff while libraries evolve continuously through breaking changes. This creates a persistent gap: the API the model reaches for may not exist in the version you have installed. The problem is worst immediately after a new major ships—when every AI-assisted user hits broken code on their first try. For maintainers, this represents an invisible support-and-perception cost that currently has no metric.

Key Insights

• {‘fact’: ‘Prisma v6 API pattern new PrismaClient({ datasources }) no longer exists in v7; model scores dropped to 80/100 (SDKProof benchmark, July 2026).’, ‘concept’: ‘Model readiness tracks drift window: newer breaking changes score worst because models haven’t absorbed them yet.’, ‘tool’: ‘SDKProof uses tsc --noEmit as ground truth judge instead of an LLM-as-judge approach.’}
• {‘fact’: ‘Vercel AI SDK renamed parameters to inputSchema and removed maxSteps in v5+; model scored only slightly better at 90/100 (SDKProof benchmark, July 2026).’, ‘concept’: ‘Prompts name functions but never option names to measure natural model reach rather than echo of prompt context.’, ‘tool’: ‘TypeScript compiler diagnostics (e.g., TS2353) classified into failure patterns for scoring.’}
• {‘fact’: ‘Zod removed required_error (now error) but retains correct usage of new two-argument z.record(); scored at top with some misses (SDKProof benchmark, July 2026).’, ‘concept’: ‘One renamed key stops the build cold even when everything else compiles cleanly.’, ‘tool’: ”}
• {‘fact’: ”, ‘concept’: ”, ‘tool’: ”}

Working Examples

Old code generated by model using v4 API - fails against ai v7

import { tool } from "ai";
import { z } from "zod";

const weatherTool = tool({
     description: "Get the weather for a city",
     parameters: z.object({ city: z.string() }), // ✗ this was the v4 API
     execute: async ({ city }) => getWeather(city),
});

Correct code using current ai v5+ API

import { tool } from "ai";
import { z } from "zod";

const weatherTool = tool({
   description: "Get the weather for a city",
   inputSchema: z.object({ city: z.string() }), // ✓ v5+
   execute: async ({ city }) => getWeather(city),
});

Practical Applications

References:

• From internal analysis