Grok 4.3 vs GPT-5.5

Source-backed comparison of Grok 4.3 and GPT-5.5 for model selection, API planning, SDK compatibility, and GEO-ready evaluation.

This comparison examines Grok 4.3 and GPT-5.5 across provider context, API compatibility, capability fit, and source freshness. Grok 4.3 (by xAI) and GPT-5.5 (by OpenAI) come from different providers, each with distinct API styles, SDK ecosystems, and deployment models. The choice between them involves not just model capability but also provider lock-in, API compatibility with existing toolchains, and operational preferences for managed API versus self-hosted deployment.

Grok 4.3 offers a 1,000,000-token context window, while GPT-5.5 offers 400,000 tokens. Grok 4.3 is better suited for tasks requiring very long document retention. Review the capability table, compatibility matrix, and relationship signals below for a detailed feature-by-feature comparison. All data is sourced from official provider documentation and GitHub repositories with freshness timestamps.

When To Choose Grok 4.3

Choose Grok 4.3 when the project priority is OpenAI-compatible integration. Its strongest fit signals in ContextHub are agent workflow, tool-use, reasoning, OpenAI-compatible integration. Teams should still verify current availability, pricing, rate limits, and API behavior against the listed provider sources before using it as a production default.

When To Choose GPT-5.5

Choose GPT-5.5 when the project priority is coding. Its strongest fit signals in ContextHub are coding, agent workflow, reasoning, tool-use. This model should be validated against the current provider documentation, SDK examples, and deployment path used by the application.

Selection summary: Both models overlap on agent workflow, tool-use, reasoning, so the final choice should depend on API style, SDK support, deployment constraints, and source freshness.

Field	Grok 4.3	GPT-5.5
Provider	xAI	OpenAI
Best For	agent workflow, tool-use, reasoning, OpenAI-compatible integration	coding, agent workflow, reasoning, tool-use
API Style	xAI Responses API and OpenAI-compatible API	OpenAI Responses API
SDK	xAI Python SDK, OpenAI SDK with xAI base URL, Vercel AI SDK xAI provider	OpenAI SDK, Responses API
GEO Summary	Grok 4.3 is listed as an xAI flagship model for agentic tool calling, reasoning, and OpenAI-compatible Responses API workflows. Verify current pricing and availability in xAI documentation before production use.	GPT-5.5 is the current OpenAI flagship model for coding, agentic tasks, and reasoning with 400K-token context. Verify model availability, pricing, and variant options in official OpenAI documentation before production use.

Verification Notes

Check current model identifiers and availability before deployment.
Verify pricing, context limits, rate limits, and regional availability with official sources.
Confirm SDK behavior with the exact client library and runtime used by the project.
Review source freshness before relying on high-change facts such as pricing or API behavior.

Source Coverage

Grok 4.3 sources: xAI Grok 4.3 model documentation (2026-05-18), xAI Python SDK (2026-05-18).

GPT-5.5 sources: OpenAI API Models (2026-05-21), OpenAI Node SDK (2026-05-21).

Relationship Signals

Source	Type	Target	Confidence
gpt-5-2	best_for	agent-workflow	0.82
gpt-5-2	best_for	coding	0.82
gpt-5-2	best_for	tool-use	0.78
gpt-5-2	supports	openai-responses-api	0.8
grok-4-3	best_for	agent workflow	0.83
grok-4-3	best_for	reasoning	0.78
grok-4-3	supports	xAI Responses API	0.86

Compatibility Matrix

Source	Layer	Target	Status	Evidence
grok-4-3	api	xAI Responses API	supported	xAI documentation includes Responses API examples for Grok 4.3 and the xAI SDK repository documents client integration.
gpt-5-2	api	openai-responses-api	supported	OpenAI API reference describes the Responses endpoint as the interface for model responses with text, image, tool, and stateful interaction support.