AI SDK 5.0.0: what breaks when you upgrade ai from 4.x

AI SDK 5 redesigned the message model, and most of what it breaks follows from that. The ai package dropped its React and RSC entrypoints, replaced the data stream API, and renamed or reshaped the types that describe a message. It also renamed the key that holds a tool’s schema and the fields on the parts streamText streams. Upgrade from 4.x and the typecheck fails on the first file that touches any of them.

What changed

• Two entrypoints left the package. ai/react is now @ai-sdk/react and ai/rsc is now @ai-sdk/rsc, same names, new dependency.
• Model message types were renamed, with aliases kept. CoreMessage is ModelMessage, the four role types gained the ModelMessage suffix, and convertToCoreMessages is convertToModelMessages. The old names still compile as deprecated aliases.
• Two renames are breaks. IDGenerator is IdGenerator, and experimental_wrapLanguageModel is exported only as wrapLanguageModel.
• UI message types changed shape. Message is UIMessage, and it has no content string: text, files and tool calls are entries in a parts array. ToolInvocation, Attachment and the CoreTool type family went with the fields they described.
• A tool’s schema key is inputSchema. parameters is a type error in v5, on the object handed to tool() and on each entry of tools handed to generateText or streamText. It is still wrong at every release up to ai@7.0.99.
• Stream parts renamed their fields. On what streamText streams, textDelta is text, args is input and result is output. tool-call-delta became tool-input-delta carrying delta, step-finish became finish-step with providerMetadata, and logprobs is gone with no replacement.
• The data stream API was replaced. StreamData and the createDataStream* helpers are gone; custom data travels as typed parts on a UI message stream. The LangChain and LlamaIndex adapters moved to their own packages. The assistant API was removed with no replacement.

Before and after

Renames with no shape change are what Emendant rewrites. This file passes one of them on without calling it, which is why the entry anchors on the import:

import { experimental_wrapLanguageModel, type IDGenerator } from 'ai';

export const wrapped = (model: never, middleware: never) =>
  experimental_wrapLanguageModel({ model, middleware });

export function label(generate: IDGenerator): string {
  return `msg_${generate()}`;
}

export const wrap = experimental_wrapLanguageModel;

After npx emendant fix:

import { wrapLanguageModel, type IdGenerator } from 'ai';

export const wrapped = (model: never, middleware: never) =>
  wrapLanguageModel({ model, middleware });

export function label(generate: IdGenerator): string {
  return `msg_${generate()}`;
}

export const wrap = wrapLanguageModel;

The tool rename is one key at each site, and the schema value stays put:

export const weather = tool({
  description: 'Look up the weather',
  parameters: schema,
  execute: async () => ({ temperature: 12 }),
});

export const weather = tool({
  description: 'Look up the weather',
  inputSchema: schema,
  execute: async () => ({ temperature: 12 }),
});

The entrypoint moves are the same edit on the specifier: 'ai/react' becomes '@ai-sdk/react' and 'ai/rsc' becomes '@ai-sdk/rsc'. Three reads off a fullStream part are one word each: part.textDelta becomes part.text, part.args becomes part.input and part.result becomes part.output. The shape changes have no mechanical form: a StreamData route becomes a writer inside createUIMessageStream, and message.content becomes the text parts of message.parts.

Migration guidance and its limits

The ten deterministic patches are safe as offered. The two entrypoint rewrites do not add @ai-sdk/react or @ai-sdk/rsc to your manifest, so install them, or the verification run reports those patches as failing until you do.

The nine assisted changes are the reshapes. Emendant writes them only when you name a model provider, because the right edit depends on how your code reads a message or builds a stream. Two of them turn on the type tag too: argsTextDelta sits in a branch v5 never enters, and experimental_providerMetadata is a rename under step-finish and a removal under finish. Without a provider they are reported with guidance. The assistant API removal and a logprobs read are report only, because nothing in v5 replaces either.

A repository on 6.x or 7.x still writing parameters is reported without --adopted, under a heading saying it is affected today.

Two limits: createIdGenerator now takes its size at creation, which the IdGenerator rename does not touch, and useChat itself changed in 5.0.0 in ways this entry does not describe. A clean scan says a file uses none of the constructs below, nothing more.

What Emendant detects, fixes and verifies

22 changes in ai 5.0.0. 10 patched by a transform, 10 patched only with a model provider you name, 2 report only. Every patch is proved in a copy of your repository before it is offered, and its header names the checks that passed. This table is generated from the feed entry, so it cannot claim more than the entry does.

emendant explain <change-id> prints any row's entry, guidance and sources at the terminal.

Coverage

Snapshot

2026-09-21.1, sequence 28, signed 21 September 2026

Minimum CLI

emendant@0.1.4

Feed entry

feed/npm/ai/5.0.0.json

emendant feed status shows the snapshot your machine holds, and emendant feed update fetches the latest.

Primary sources

Every claim above was checked against these, each pinned to the release rather than to a default branch.

• Migration guidevercel/ai at ai@5.0.0
• package.jsonvercel/ai at ai@5.0.0
• ai@5.0.0npm registry, the published package
• ai@4.0.0npm registry, the published package
• ai@7.0.99npm registry, the published package

Scan your repository

Runs locally, reads your lockfile and source, sends nothing anywhere.

npx emendant scan

Then npx emendant fix writes the patches the table says exist. The getting started guide covers the flags and the patch grades.