Durable Objects sharing one isolate are each billed for 128 MB
David Matějka (@matej_21) points out that several Durable Objects can be placed in one 128 MB isolate while each active object is still billed as 128 MB.
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- Durable Objects
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- David Matějka (@matej_21)
Key points
- He writes that Cloudflare can place multiple Durable Object instances into a single 128 MB V8 isolate while billing each active object as if it had 128 MB allocated, so four active objects sharing one isolate are effectively billed for 512 MB.
- He adds that you do not control placement, that how instances are packed is not documented, and that if one object pushes the shared isolate over 128 MB the whole isolate is retired: shared memory, dedicated-memory pricing and a shared failure domain.
- Official docs (rechecked 2026-10-16): duration billing charges for the 128 MB allocated regardless of actual usage; objects of the same class may run in the same isolate and share 128 MB, and are still billed as if each had a full 128 MB.
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Read on 𝕏David Matějka (@matej_21) points out that several Durable Objects can be placed in one 128 MB isolate while each active object is still billed as 128 MB.
David Matějka
@matej_21 · Original 𝕏 post
Did you know Cloudflare can place multiple Durable Object instances into a single 128 MB V8 isolate? Did you also know Cloudflare bills each active DO as if it had 128 MB of memory allocated? 4 active DOs can share same 128 MB isolate, while you're effectively paying for 512 MB. You don't control the placement, and Cloudflare doesn't document how instances are packed. And if a single DO pushes that shared isolate over 128 MB, the whole isolate gets retired. Shared memory, dedicated-memory pricing, opaque scheduling, shared failure domain. I really hope this changes, especially now that Cloudflare is pushing Durable Objects harder than ever.
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