Independent guide. Not affiliated with SpaceXSI, xAI or X.
Home/Grok models/Grok Heavy
Grok models

Grok Heavy: how the multi-agent version works and who can use it

What Grok Heavy does, how it grew from Grok 4 Heavy to the 16-agent Grok 4.20 Heavy, and what the October 2026 plan change means.

Checked October 18, 2026By GrokMag editorsIndependent · not affiliated with SpaceXSI, xAI or X
Short answer

Grok Heavy runs several agents in parallel on one problem and combines their answers. It began as Grok 4 Heavy in July 2025 on the $300 SuperGrok Heavy plan. Grok 4.20 uses 4 agents, or 16 in Heavy. On the API the model is grok-4.20-multi-agent-0309. Which X Subscription tier includes Heavy after October 12, 2026 is not stated by SpaceXSI.

What Grok Heavy is

Grok Heavy is the multi-agent version of a Grok model. Instead of one model answering, several agents work on the same problem in parallel. Their answers are then compared and combined into one response. The idea is that independent attempts catch each other’s mistakes on hard questions.

The trade-off is cost. Running several agents uses several times the compute of a single answer, which is why Heavy has always sat at the top of the price list. Our glossary entry gives the short version.

From Grok 4 Heavy to Grok 4.20

Grok 4 Heavy (July 2025)

SpaceXSI (formerly xAI) launched Grok 4 Heavy alongside Grok 4 on July 9, 2025. It was sold through the SuperGrok Heavy plan at $300 per month. At launch the company claimed a score of 44.4% on Humanity’s Last Exam, a test made of very hard expert questions. That is a vendor claim.

Grok 4.20 (February 2026)

Grok 4.20 entered beta on February 17, 2026, and was built on a four-agent system from the start. A Heavy version scales that to 16 agents. Community reports name the four agents:

  • Grok: coordinator
  • Harper: research
  • Benjamin: logic, math and code
  • Lucas: contrarian
Unofficial names: these agent names come from community reports. SpaceXSI has not officially published them, so treat them as reported, not confirmed.

Grok 4.20 reached the API on March 10, 2026, with a 1M-token context window, in reasoning, non-reasoning and multi-agent versions.

Multi-agent Grok on the API

Developers do not need a consumer plan to use multi-agent Grok. The API model is grok-4.20-multi-agent-0309. As of October 18, 2026, it is priced the same as the other Grok 4.20 models:

ModelContextInput / cached / output200k+ prompts
grok-4.20-multi-agent-03091M$1.25 / $0.20 / $2.50$2.50 / $0.40 / $5.00

Prices are USD per million tokens. The Batch API takes 20% off for the three grok-4.20-0309 models and grok-4.3. Batch calls also do not count toward rate limits. There is no Heavy version of Grok 4.7 on the API’s model list.

Which plan gets Heavy now

This is unclear, and we would rather say so than guess.

  • Before October 12, 2026: Heavy belonged to SuperGrok Heavy at $300 per month.
  • After October 12, 2026: the new X Subscription tiers (Free, Plus $8, Premium $30, Super $100, Ultra $200) replaced SuperGrok for new buyers. The official pricing page does not mention “Heavy” at all. The closest items are “cloud agents and automations” on Premium and above.
  • Existing subscribers: legacy plans, including SuperGrok Heavy, continue for people who already have them. The Grok FAQ still refers to SuperGrok Heavy yearly invoices.
Before you pay: no official page says which X Subscription tier includes Grok Heavy. Ask SpaceXSI support or check the model picker in your app before upgrading for Heavy alone. Our free vs paid guide covers what each tier does list.

Heavy vs other multi-agent Grok products

SpaceXSI now runs several products that use more than one agent. They are easy to confuse.

ProductWhat runs in parallelBest for
Grok HeavySeveral agents answer one question, then merge resultsHard reasoning questions
Grok BuildCoding subagents, each with its own context windowSoftware work in a terminal
Grok BotNamed Bots on a shared cloud computerOngoing tasks in your apps and browser

Grok Bot itself launched in August 2026 for SuperGrok Heavy subscribers and some Cursor plans before it opened to more tiers. It is now included from Premium ($30) up.

Questions people ask

How much does Grok Heavy cost?

It used to come with SuperGrok Heavy at $300 per month. Since October 12, 2026, SpaceXSI has not said which X Subscription tier includes it. On the API, grok-4.20-multi-agent-0309 costs $1.25 per million input tokens and $2.50 per million output tokens.

How many agents does Grok Heavy use?

Grok 4.20 uses four agents, and its Heavy version uses 16, according to a guide to the system. The names of the four agents are community-reported, not official.

Is SuperGrok Heavy still available?

Not for new buyers. Existing subscribers keep it, but new customers choose from the X Subscription tiers. See Grok Bot pricing for how the tiers compare.

Is there a Grok 4.7 Heavy?

Not on the API model list as of October 18, 2026. The only multi-agent API model is grok-4.20-multi-agent-0309.

Current flagshipGrok 4.7: specs, price and benchmarksRead it →All modelsEvery Grok model in one tableRead it →AgentsHow Grok Bot worksRead it →
Sources (checked October 18, 2026)
  1. Verdent guide to the Grok 4.20 multi-agent system (fetched Oct 18, 2026)
  2. SpaceXSI release notes (fetched Oct 18, 2026)
  3. SpaceXSI API pricing (fetched Oct 18, 2026)
  4. Keywords AI on Grok 4 and Grok 4 Heavy (Jul 16, 2025)
  5. X Subscription pricing (fetched Oct 18, 2026)
  6. SpaceXSI: The X Subscription (Oct 12, 2026)
  7. Grok FAQ (fetched Oct 18, 2026)
  8. AI Subscription Comparison: Grok tiers (verified Apr 17, 2026)
  9. GIGAZINE on the Grok Bot launch (Aug 12, 2026)
  10. SpaceXSI: Grok Bot (fetched Oct 18, 2026)