> For the complete documentation index, see [llms.txt](https://spire-docs.gitbook.io/spire/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://spire-docs.gitbook.io/spire/pylon/faqs.md).
# FAQs
What is the roadmap for based appchains?How do synchronously composable transactions work?
Pylon runs a node for the settlement chain you are deployed to as well as the sequencing node for your appchain and any other appchains in your [Sync Zone](/spire/pylon/architecture-overview.md#sync-zones). Pylon then detects whenever there is a transaction calling into another chain through a [Port Contract](/spire/pylon/architecture-overview.md#port-contracts). It forwards the call to the other chain and then injects the results back into the originating Port contract with a Priming Transaction that frontruns the original application call to ensure the data is available to complete the call. See [Synchronously Composable Transactions](/spire/pylon/features.md#synchronously-composable-transactions) for details.
How can I trust the data being injected into the port contract?
We are working on a TEE based proof process that will ensure data moving across chains is verifiably correct with the speed to ensure a seamless experience. We will be releasing more about this soon!
What are the trust assumptions for the chain itself?
We currently run a reth stack based system. So the trust assumptions for the chain are fraud proof based and of course impacted by the parent chain you deploy on. Due to the requirement for coordinated sequencing within a [Sync Zone](/spire/pylon/architecture-overview.md#sync-zones) and the current architecture all appchain sequencers within a [Sync Zone](/spire/pylon/architecture-overview.md#sync-zones) run on a single node. Standard nodes for a given appchain (such as for submitting fraud proofs) can be operated by anyone.
What stacks/settlement chains are supported?
Currently we support any op-stack settlement chains but are working on adding support for additional chains. Even if your targeted settlement chain is not already supported we'd love to speak with you about getting your use-case supported. Please reach out through [this form](https://docs.google.com/forms/d/e/1FAIpQLSdgl5fFhevRbIabnfBBCtb_S2hRbHe27ighW6QMxwiH8jAfpA/viewform?usp=sf_link).
What fees are there?
Please reach out to discuss through [this form](https://docs.google.com/forms/d/e/1FAIpQLSdgl5fFhevRbIabnfBBCtb_S2hRbHe27ighW6QMxwiH8jAfpA/viewform?usp=sf_link)!
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