Grok 4.5 vs Grok 4.3: API Model Selection and Migration Guide

Short answer: start with Grok 4.5 when a difficult coding change, long agent loop, or knowledge-work deliverable makes quality and reasoning headroom more important than the lowest token rate. Keep or choose Grok 4.3 when the workload needs its 1-million-token context window, optional non-reasoning mode, lower input and output prices, the current xAI eu-west-1 route, or the model-specific Batch discount.

These are two API model versions inside the Grok and xAI developer ecosystem, not separate products to buy. Product subscriptions and API billing are different decisions. Use Grok pricing for maintained prices and access routes, then Grok subscription vs xAI API pricing when the real question is app access versus separately metered API use.

Decision by workload

This is a conditional recommendation, not a claim that every Grok 4.5 response will beat Grok 4.3. xAI’s launch evaluations support the newer model’s coding and agentic positioning, but they are vendor-reported results produced with particular harnesses and settings. The defensible production choice is the least expensive route that passes the same task-success, evidence, tool-use, latency, and recovery-cost tests.

What changes and what does not

The context difference is a real capacity boundary. Grok 4.5 is not a blanket successor for requests that rely on the upper half of Grok 4.3’s window. xAI also does not publish a separate maximum-output figure on either public model card, so do not convert the total context number into an invented output ceiling.

Reasoning behavior creates the largest drop-in risk. The live Grok 4.3 model card lists four levels without stating the implicit default, while Grok 4.5 explicitly defaults to high. Do not let an omitted setting or documentation drift decide production behavior: set matched low, medium, or high effort during evaluation. A Grok 4.3 route using none still has no exact Grok 4.5 equivalent because reasoning cannot be disabled.

“Agentic” also does not mean that every adjacent API capability automatically carries over. Current official guides provide evidence for both models across Web Search, X Search, code execution, file attachment search, collections search, and remote MCP, in addition to function calling and structured outputs. That is evidence for those named paths only. Built-in tools are documented through the Responses API or xAI SDK, while custom function calling and structured outputs also have Chat Completions paths; test the exact endpoint and tool combination instead of inferring universal parity.

Token prices, long context, and caching

Standard token prices are in USD per 1 million tokens:

Grok 4.5 therefore costs 1.6 times as much for uncached input, 2.5 times as much for cached input, and 2.4 times as much for output before reasoning volume and tool calls are counted. Reasoning tokens are billed at the output rate, so effort and reasoning volume can widen the gap. The premium can still be economical if it avoids retries or review, but the model name alone does not prove a lower completed-task cost.

Both model-detail payloads set a 200,000-token long-context threshold and double input, cached-input, and output rates in the higher-context tier:

Official wording is inconsistent at the exact edge: model-page prose says higher pricing applies when prompt tokens exceed 200K, while the Models REST schema defines the threshold as applying at or above its value. Treat 200,000 tokens as a billing boundary, log actual prompt and cost data, and leave headroom rather than designing a router that depends on one token at the edge. The higher rate applies to the whole request tier, not only to tokens beyond the boundary.

Prompt caching reuses an exact prefix from earlier requests. Grok 4.5’s guide recommends a stable prompt_cache_key in the Responses API or x-grok-conv-id in Chat Completions so related requests are more likely to reach the same server. Cache hits are not guaranteed, so cost models should use observed cached-token counts rather than an assumed hit rate.

The published cached rate is 25% of uncached input for Grok 4.5 and 16% for Grok 4.3. xAI does not publish a separate cache-write line item for either model. Budget the first pass at the normal input rate and apply the cached rate only to reused prefix tokens that the response actually reports as cached.

Batch and service-tier economics

The Batch API is for asynchronous work that usually finishes within 24 hours, although xAI calls that timing best effort rather than guaranteed. Batch requests do not consume the normal per-minute inference limits, and the API can process Chat Completions or Responses requests with server-side and client-side tools subject to tool-specific constraints.

The 20% Grok 4.3 discount applies to input, cached, output, and reasoning tokens; xAI does not state that separate server-side tool invocation fees receive the same discount. The live Batch guide explicitly submits Grok 4.5 requests, so current official documentation supports Batch eligibility. The pricing page says models not listed receive no Batch discount, and Grok 4.5 is not listed; its Batch work is billed at normal model rates. Preflight the exact model, endpoint, tools, and account before building a production queue.

Priority Processing answers a different question. It requests higher scheduling priority for interactive Responses or Chat Completions traffic and charges twice the applicable token rates only when the response confirms the priority tier. It is not available inside Batch. Do not upgrade to Grok 4.5 merely to solve a scheduling problem, and do not move a latency-sensitive request to Grok 4.3 merely because its tokens are cheaper.

Tools, structured outputs, and search

Both models have official evidence for function calling and structured outputs. xAI’s structured-output contract can enforce a supported JSON Schema subset, while custom function arguments are generated against the supplied tool schema. Preserve schema validation and business-level validation in the application: syntactic conformance does not prove that extracted facts or chosen actions are correct.

Web Search, X Search, and code execution are documented server-side tools, and their invocation charges sit on top of model tokens. Web Search and X Search are each $5 per 1,000 calls; code execution is also $5 per 1,000 calls. File attachment search and collections search use different rates, while remote MCP execution is token-billed rather than assigned the same search-call fee. Use Grok Web Search vs X Search when the next decision is which evidence domain and filter set the agent needs.

Do not equate one user request with one paid tool call. The model can call a server-side tool multiple times, and reasoning or retrieved content can increase token usage. Compare end-to-end request cost with tool counts included. For current-event work, neither model has realtime knowledge without search or supplied retrieval, so a newer training run does not replace Web Search, X Search, or source verification.

A safe compatibility claim is still narrow: both models have official evidence for the two core text endpoints, function calling, structured output capability, Web Search, X Search, code execution, files, collections, and remote MCP. Tool availability does not erase endpoint or workflow limits. File attachment search is agentic rather than a batch-style n-generate path, remote MCP supports specific transports, and mixed or multi-turn tool loops still need application handling. Run model-specific acceptance tests instead of treating a shared feature name as behavioral parity.

Aliases, regions, and lifecycle

Use explicit model names during migration. The current alias map assigns grok-4.5-latest and grok-build-latest to Grok 4.5, while grok-4.3-latest and the broad grok-latest alias resolve to Grok 4.3. Calling grok-latest therefore does not currently select the newest numbered model. Alias ownership can change, so log the returned model and system fingerprint and re-run evaluations before adopting a moving alias.

Neither public model card lists a dated snapshot. Do not describe grok-4.5 or grok-4.3 as permanently pinned behavior merely because the names lack “latest.” Teams that need auditability should save request settings, response metadata, prompts, tool schemas, and evaluation results, then keep a rollback route ready.

Regional availability can block an otherwise sound upgrade. Grok 4.5’s official launch material says it is not yet available in the xAI API console for EU users and describes access as expected later. Its xAI model page currently exposes two US clusters. Grok 4.3 is present in xAI’s eu-west-1 model data as well as US data. Partner gateways can have different regions and terms, so check the exact provider, team console, and data-residency path rather than treating a planned rollout as completed availability.

The current retirement notice removes several earlier Grok slugs and redirects most of them to Grok 4.3; it does not name Grok 4.3 for retirement. That supports keeping 4.3 as a valid rollback today, not assuming indefinite support. Recheck release notes and retirement guidance before every migration window.

Migration plan

1. Inventory the real route. Record the exact model or alias, endpoint, region, reasoning effort, cache-routing key, service tier, tools, schemas, context length, and fallback behavior. Resolve moving aliases before comparing results.
2. Freeze a Grok 4.3 baseline. Capture representative easy, normal, hard, long-context, and failure-prone requests. Measure final task success, instruction following, evidence quality, structured-output validity, tool completion, retries, reasoning and output tokens, latency, cache hits, tool calls, and total billed cost.
3. Shadow Grok 4.5 at matched effort. Start with the same explicit low, medium, or high setting instead of comparing implicit Grok 4.3 behavior with Grok 4.5’s default high. Test high separately when its added reasoning is part of the business case. A none-effort 4.3 workload needs a separate decision because 4.5 cannot reproduce that mode.
4. Split the context evaluation. Test ordinary prompts below the higher-price boundary, prompts near 200,000 tokens, and the longest real requests. Keep any request above 500,000 tokens on Grok 4.3 or redesign it with retrieval or compaction; Grok 4.5 cannot accept the published 4.3 maximum.
5. Re-run every integration. Validate Responses and Chat Completions payloads, structured schemas, function loops, Web Search, X Search, code execution, remote MCP, files or collections, streaming, error handling, and Batch submission that the application actually uses. Do not infer support from adjacent examples.
6. Canary with explicit rollback. Route a small, observable share to Grok 4.5, keep Grok 4.3 callable, and set failure, cost, latency, and quality thresholds. Promote hard workloads only when 4.5 earns its premium; leave low-risk, long-context, xAI-EU-cluster-bound, non-reasoning, or discounted offline traffic on 4.3 when that route passes.

The practical boundary is workload evidence. Grok 4.5 is the stronger starting hypothesis for hard coding, agentic, and knowledge work. Grok 4.3 remains the rational route for lower unit cost, 1-million-token capacity, optional zero reasoning, the current xAI eu-west-1 route, and discounted Batch traffic. A mixed router can be more defensible than a universal migration.