diff --git a/abci/client/unsync_local_client.go b/abci/client/unsync_local_client.go
new file mode 100644
index 00000000000..da77b56d2fd
--- /dev/null
+++ b/abci/client/unsync_local_client.go
@@ -0,0 +1,136 @@
+package abcicli
+
+import (
+	"context"
+	"sync"
+
+	"github.com/cometbft/cometbft/abci/types"
+	"github.com/cometbft/cometbft/libs/service"
+)
+
+type unsyncLocalClient struct {
+	service.BaseService
+
+	types.Application
+
+	mtx sync.Mutex
+	Callback
+}
+
+var _ Client = (*unsyncLocalClient)(nil)
+
+// NewUnsyncLocalClient creates a local client, which wraps the application
+// interface that Comet as the client will call to the application as the
+// server.
+//
+// This differs from [NewLocalClient] in that it returns a client that only
+// maintains a mutex over the callback used by CheckTxAsync and not over the
+// application, leaving it up to the proxy to handle all concurrency. If the
+// proxy does not impose any concurrency restrictions, it is then left up to
+// the application to implement its own concurrency for the relevant group of
+// calls.
+func NewUnsyncLocalClient(app types.Application) Client {
+	cli := &unsyncLocalClient{
+		Application: app,
+	}
+	cli.BaseService = *service.NewBaseService(nil, "unsyncLocalClient", cli)
+	return cli
+}
+
+func (app *unsyncLocalClient) SetResponseCallback(cb Callback) {
+	app.mtx.Lock()
+	app.Callback = cb
+	app.mtx.Unlock()
+}
+
+func (app *unsyncLocalClient) CheckTxAsync(ctx context.Context, req *types.RequestCheckTx) (*ReqRes, error) {
+	res, err := app.Application.CheckTx(ctx, req)
+	if err != nil {
+		return nil, err
+	}
+	return app.callback(
+		types.ToRequestCheckTx(req),
+		types.ToResponseCheckTx(res),
+	), nil
+}
+
+func (app *unsyncLocalClient) callback(req *types.Request, res *types.Response) *ReqRes {
+	if app.Callback != nil {
+		app.Callback(req, res)
+	}
+	rr := newLocalReqRes(req, res)
+	rr.callbackInvoked = true
+	return rr
+}
+
+// -------------------------------------------------------
+
+func (*unsyncLocalClient) Error() error {
+	return nil
+}
+
+func (*unsyncLocalClient) Flush(context.Context) error {
+	return nil
+}
+
+func (*unsyncLocalClient) Echo(_ context.Context, msg string) (*types.ResponseEcho, error) {
+	return &types.ResponseEcho{Message: msg}, nil
+}
+
+func (app *unsyncLocalClient) Info(ctx context.Context, req *types.RequestInfo) (*types.ResponseInfo, error) {
+	return app.Application.Info(ctx, req)
+}
+
+func (app *unsyncLocalClient) CheckTx(ctx context.Context, req *types.RequestCheckTx) (*types.ResponseCheckTx, error) {
+	return app.Application.CheckTx(ctx, req)
+}
+
+func (app *unsyncLocalClient) Query(ctx context.Context, req *types.RequestQuery) (*types.ResponseQuery, error) {
+	return app.Application.Query(ctx, req)
+}
+
+func (app *unsyncLocalClient) Commit(ctx context.Context, req *types.RequestCommit) (*types.ResponseCommit, error) {
+	return app.Application.Commit(ctx, req)
+}
+
+func (app *unsyncLocalClient) InitChain(ctx context.Context, req *types.RequestInitChain) (*types.ResponseInitChain, error) {
+	return app.Application.InitChain(ctx, req)
+}
+
+func (app *unsyncLocalClient) ListSnapshots(ctx context.Context, req *types.RequestListSnapshots) (*types.ResponseListSnapshots, error) {
+	return app.Application.ListSnapshots(ctx, req)
+}
+
+func (app *unsyncLocalClient) OfferSnapshot(ctx context.Context, req *types.RequestOfferSnapshot) (*types.ResponseOfferSnapshot, error) {
+	return app.Application.OfferSnapshot(ctx, req)
+}
+
+func (app *unsyncLocalClient) LoadSnapshotChunk(ctx context.Context,
+	req *types.RequestLoadSnapshotChunk) (*types.ResponseLoadSnapshotChunk, error) {
+	return app.Application.LoadSnapshotChunk(ctx, req)
+}
+
+func (app *unsyncLocalClient) ApplySnapshotChunk(ctx context.Context,
+	req *types.RequestApplySnapshotChunk) (*types.ResponseApplySnapshotChunk, error) {
+	return app.Application.ApplySnapshotChunk(ctx, req)
+}
+
+func (app *unsyncLocalClient) PrepareProposal(ctx context.Context, req *types.RequestPrepareProposal) (*types.ResponsePrepareProposal, error) {
+	return app.Application.PrepareProposal(ctx, req)
+}
+
+func (app *unsyncLocalClient) ProcessProposal(ctx context.Context, req *types.RequestProcessProposal) (*types.ResponseProcessProposal, error) {
+	return app.Application.ProcessProposal(ctx, req)
+}
+
+func (app *unsyncLocalClient) ExtendVote(ctx context.Context, req *types.RequestExtendVote) (*types.ResponseExtendVote, error) {
+	return app.Application.ExtendVote(ctx, req)
+}
+
+func (app *unsyncLocalClient) VerifyVoteExtension(ctx context.Context, req *types.RequestVerifyVoteExtension) (*types.ResponseVerifyVoteExtension, error) {
+	return app.Application.VerifyVoteExtension(ctx, req)
+}
+
+func (app *unsyncLocalClient) FinalizeBlock(ctx context.Context, req *types.RequestFinalizeBlock) (*types.ResponseFinalizeBlock, error) {
+	return app.Application.FinalizeBlock(ctx, req)
+}
diff --git a/proxy/client.go b/proxy/client.go
index 97f10673327..b94910db67d 100644
--- a/proxy/client.go
+++ b/proxy/client.go
@@ -69,6 +69,30 @@ func (c *connSyncLocalClientCreator) NewABCIClient() (abcicli.Client, error) {
 	return abcicli.NewLocalClient(nil, c.app), nil
 }
 
+// -----------------------------------------------------------------------------
+// most advanced local client creator with a more complex concurrency model
+// than the other local client creators - all concurrency is assumed to be
+// handled by the application
+
+type unsyncLocalClientCreator struct {
+	app types.Application
+}
+
+// NewUnsyncLocalClientCreator returns a [ClientCreator] that is fully
+// unsynchronized, meaning that all synchronization must be handled by the
+// application. This is an advanced type of client creator, and requires
+// special care on the application side to ensure that consensus concurrency is
+// not violated.
+func NewUnsyncLocalClientCreator(app types.Application) ClientCreator {
+	return &unsyncLocalClientCreator{
+		app: app,
+	}
+}
+
+func (c *unsyncLocalClientCreator) NewABCIClient() (abcicli.Client, error) {
+	return abcicli.NewUnsyncLocalClient(c.app), nil
+}
+
 //---------------------------------------------------------------
 // remote proxy opens new connections to an external app process